This invention relates to polyamide-based thermoplastic formulations having improved melt-flow characteristics. Two of the most commercially significant polyamides are poly(hexamethyleneadipamide) and polycaprolactam. These two polyamides are commonly referred to, respectively, as nylon 6,6 and nylon 6.
Both nylon 6,6 and nylon 6 are used in thermoplastic formulations to produce injection molded and extruded articles. In these uses, the melt-flow characteristics of the formulation are important to the article manufacturer. In both injection molding and extrusion, a formulation having a low flow rate, under processing conditions, can result in only partial formation of the article as the formulation does not completely fill the mold or flow evenly through the extruder during the cycle time allotted.
The melt-flow characteristics of thermoplastic formulations are commonly quantified and reported as the melt index in grams/ten minutes as measured under ASTM D 1238-79. A typical melt index for nylon 6,6 is 12 grams/10 minutes. Additives, such as o- or p- toluene sulfonamide may be used to improve the melt index, but such additives can increase the flammability of the formulation or adversely affect the physical properties of articles made from such formulations.
It is common practice to use reinforcing fillers in nylon 6,6 and nylon 6 formulations to increase the tensile and flexural strengths of articles produced therefrom. Glass fibers are commonly used as the reinforcing filler, especially chopped glass fibers about 3 mm long. The glass fiber loading is from about 5-50 weight percent of the formulation, and most often, 30-33 weight percent. While glass fiber is useful in enhancing tensile and flexural strengths, its presence in the formulation significantly degrades its melt-flow characteristics. A typical value for glass fiber reinforced nylon 6,6 is 7 grams/10 minutes as measured by ASTM D 1238-79. Thus, formulations based upon glass reinforced nylon 6,6 or nylon 6 can be very difficult to mold or extrude.